(1) Technical Field
This invention relates to a liquid crystal display element used for liquid crystal displays, optical shutters, and the like and to a producing method thereof.
(2) Description of the Prior Art
Liquid crystal panels used for the liquid crystal display elements, offering advantages of low-profile, weight saving, low voltage drive-ability and the like, are used for watches, electronic calculators, personal computers, personal word processors and the like.
The TN (Twisted Nematic) type liquid crystal panel is typically used therefore, adopting an operation mode in which electrodes are formed on upper and lower substrates so that liquid crystals can be allowed to switch with application of a vertical electric field vertical to the substrates.
On the other hand, a horizontal electric field application mode has been proposed for expanding the viewing angle of the liquid crystal panel. The horizontal electric field application mode in which pixel electrodes and common electrodes are formed on the same substrate so that liquid crystal molecules can be allowed to operate with application of a horizontal electric field. This application mode is called the IPS (In-Plane-Switching) mode or the comb electrode operation mode (Cf. Liquid Crystal Display Technique: Sangyo Tosho p42).
Modification of the IPS mode has also been proposed, including the FFS mode (Fringe Field Switching Mode) in which the distance between the electrodes is narrowed for driving the liquid crystals and the HS mode (Hybrid Switching Mode)(see FIG. 57) in which the electrodes are formed on the opposing substrate side to use an oblique electric field. In these modified modes also, the horizontal electric field is generated on a plane of the substrate. Accordingly, these oblique electric field application modes are also called herein the horizontal electric field application mode.
Shown in FIGS. 1 and 2 are structural diagrams of a conventional IPS mode of liquid crystal panel. It is supposed herein that the liquid crystal molecules as are initially aligned in parallel to common electrode parts 6 . . . (or pixel electrode parts 8 . . . ) are aligned vertically to the common electrode parts 6 . . . (or the pixel electrode parts 8 . . . ) when a voltage is applied to the common electrode parts 6 . . . and the pixel electrode parts 8 . . . . It is to be noted that the same functional members as those of the present invention described below are designated by the same reference numerals.
In the conventional horizontal electric field application mode, since the common electrode parts 6 . . . and the pixel electrode parts 8 . . . have a flat plate-like shape and a square shape in section, the horizontal electric field is not applied so much to the liquid crystal molecules on the common electrode parts 6 . . . and the pixel electrode parts 8 . . . . Due to this, the conventional horizontal electric field application mode has the problem that the liquid crystals 12 are not allowed to fully operate with application of a voltage, as shown in FIG. 3. Also, since the common electrode parts 6 . . . and the pixel electrode parts 8 . . . of the conventional horizontal electric field application mode are formed of metal such as Al, light is not allowed to pass through the parts over the electrode parts 6 . . . and 8 . . . . Although the liquid crystal molecules over the both electrode parts 6 . . . and 8 . . . are not allowed to operate, since light does not pass through the parts over those electrodes and thus those parts are invisible, this has not been treated as the problem so far.
In consideration of these problems, the method for suppressing reflection over the electrodes in the reflective liquid crystal panel by forming the both electrode parts from transparent conducting material has been proposed (C. Japanese Patent Application Laying open No. 9(1997)-61842). However, since the horizontal electric field is not fully applied to the liquid crystal molecules over the both electrode parts, as mentioned above, the liquid crystal molecules do not operate in the horizontal direction and no effect is produced by simply making the both electrode parts transparent.
Another method has been proposed (Cf. Japanese Patent Application Laying open No. 9(1997)-171194) in which the pixel electrode parts and the common electrode parts are formed into a curved form in section. This proposal aims to provide improved rising characteristics of the liquid crystals with continuous application of the electric field. This is because the vertical electric field is so strong that the horizontal electric field cannot fully be applied to the liquid crystals. However, substantial improvement in operation of liquid crystal molecules over the both electrode parts cannot be achieved by simply forming the both electrode parts into the curved section. Also, since this proposed method has no intention of making the both electrodes transparent, improvement in aperture ratio cannot be achieved, either. In addition, this method of forming the both electrode parts themselves into the curved form in section has the additional problem of production difficulty.
Further, still another method has been proposed (Cf. Japanese Patent Application Laying open No. 8(1996)-286211) in which one of the pixel electrode parts and the common electrodes are formed into an inverted V-shape such that reflection by the surfaces of the electrodes can allow incident light to be gathered into their apertures. However, since the electrodes require light to be gathered into the apertures, the electrodes cannot be formed by the transparent electrodes. On the contrary, they are formed of high reflectivity material such as Al, Cu or the like. Because of this, improved aperture ratio cannot be produced. Besides, since the light must be entered from a direction of an apex of the V-shape, this method involves many practical problems. In addition, since the reflective surfaces of the electrodes have an inverted V-shape or an inverted U-shape in section, as shown in FIG. 4, the outgoing angle (xcex80 of FIG. 4) is limited to a definite range by a cone angle xcex1 of the inverted V shape or inverted U shape, so that the viewing angle is narrowed. In other words, according to the liquid crystal display element mentioned above, since the reflective surface having the inverted V-shaped or inverted U-shaped section produces directed reflected light and sets limits to the viewing angle, there remains the problem that the horizontal electric field application mode (IPS) cannot fully bring out its advantage of expanding the viewing angle.
Furthermore, yet another method has been proposed (Cf. Japanese Patent Application Laying open No. 9(1997)-258265) in which the pixel electrode parts and the common electrode parts are formed on top surfaces and slant surfaces of layer insulation films. However, this proposal described clearly that the both electrode parts are not made transparent. Also, this proposal is totally silent about improvement in speed of response.
Accordingly, it is an object of the present invention to provide a liquid crystal display element and a producing method thereof that can be intended to produce improved display characteristics by an application of horizontal electric field to liquid crystals over electrodes to a sufficient extent.
It is another object of the present invention to provide a liquid crystal display element and a producing method thereof that can produce a bright display by improvement in aperture ratio and also increased speed of response.
Further, it is still another object of the present invention to provide a liquid crystal display element and a producing method thereof that can produce a broad viewing angle.
The above-mentioned objects can be accomplished by the present invention which provides a liquid crystal display element comprising a liquid crystal panel which comprises a pair of substrates and liquid crystals sealed off in between the pair of substrates and which changes alignment of the liquid crystals by a horizontal electric field being generated in a plane of one of the pair of substrates, wherein a plurality of striped projections and depressions are formed on the plane of the substrate in which the horizontal electric field is generated; wherein pixel electrode parts of pixel electrodes and common electrode parts of common electrodes are alternately formed on either only side faces of striped projection parts of the striped projections and depressions or the side faces and top portions of the striped projection parts of the striped projections and depressions; and wherein at least one of the pixel electrode parts and the common electrode parts is transparent.
With this construction, in which the pixel electrode parts and the common electrode parts are formed on only side faces of striped projection parts of the striped projections and depressions or on the side faces and top portions of the striped projection parts of the striped projections and depressions, the electric field is also applied to a region over the both electrodes parts (i.e., the horizontal electric field to a sufficient extent). This enables the liquid crystal molecules over the both electrodes to be activated to thereby produce improved display characteristics. Also, since at least one of the both electrodes is transparent, light is prevented from being cut off by the electrode parts. This can produce significantly improved aperture ratio and also can prevent decrease in the aperture ratio even when the distances between the electrode parts are narrowed. This enables the distances between the electrodes to be narrowed, thus producing increased speed of response of the liquid crystals.
The pixel electrode parts and the common electrode parts should be formed on only side faces of striped projection parts, rather than on the side faces and top portions of the striped projection parts of the striped projections and depressions. This is because, when the pixel electrode parts are formed on the top portions of the striped projection parts as well, the electric field is applied upwardly (vertically), while on the other hand, when the pixel electrode parts are formed on only the side faces of the striped projection parts, the electric field is applied solely across the pixel electrode parts and the common electrode parts (only in a horizontal direction).
The striped projections and depressions may be formed on an insulation film.
The insulation film may be composed of a color filter layer.
This structure can eliminate the need to form an additional color filter and thus can eliminate the need for any margin for sticking the color filter on, thus producing further increased aperture ratio.
The insulation film may be transparent.
This structure is capable for a transmission liquid crystal display element and also can prevent decrease in the aperture ratio.
Preferably, the insulation film have a film thickness of 1 xcexcm or more.
The reasons for this limitation are that the film thickness of the insulation film of 1 xcexcm or more can substantially absorb irregularity of a surface of the substrate forming thereon the insulation film to produce a smooth surface of the insulation film and that the film thickness of 1 xcexcm or more is desirable for reliable insulation performance of the insulation film.
In a case where the pixel electrode parts and the common electrode parts are alternately formed on the side faces of the striped projection parts of the striped projections and depressions, a distance between two adjoining electrode parts at the top of each striped projection part is preferably limited to not more than 6 xcexcm.
The reason for this limitation is that when the distance between the two adjoining electrodes exceeds 6 xcexcm, the both electrode parts are too short to allow the electric field to be applied across them to a sufficient extent.
An aspect ratio in the striped projection part may be limited to be not more than 2.5, or preferably not more than 1.5.
The reason for this limitation is that when the aspect ratio exceeds 2.5, opposing areas of the both electrode parts are reduced, such that the horizontal electric field is not applied so much across the both electrode parts.
A ratio of a length of the pixel electrode parts or common electrode parts to a length of an oblique plane of the striped projections and depressions may be limited to not more than 0.5.
The reason for this limitation is than when the ratio of a length of the pixel electrode parts or common electrode parts to a length of an oblique plane of the striped projections and depression exceeds 0.5, the state of the horizontal electric field is sometimes disordered.
Light may be allowed to enter from an array substrate side of the both substrates.
A liquid crystal display element may include multiple layers of liquid crystal panels.
The above-mentioned objects can be accomplished by the present invention which provides a method of producing a liquid crystal display element comprising a first step of forming scan signal lines, video signal lines and semiconductor layers on one of a pair of substrate; a second step of forming an insulation layer having thereon a plurality of projections and depressions on the scan signal lines, the video signal lines and the semiconductor layers; and a third step of forming pixel electrode parts of pixel electrodes and common electrode parts of common electrodes, at least one of which is transparent, on only side faces of striped projection parts of the striped projections and depressions or on the side faces and top portions of the striped projection parts of the striped projections and depressions.
With this method, since the striped projections and depressions (curved section) are formed on the insulation film which is the base of the both electrode parts, rather than the both electrode parts themselves being formed to have a curved section, the liquid crystal display element capable of producing the operation and effect as set forth in Embodiment 1 can be produced with ease.
In the second step of the above-mentioned method, said insulation film is formed by photosensitive resin being applied and then subjected to exposure while or after being pressed by a mold having thereon projections and depressions.
The process step as mentioned above can facilitate the production of the insulation film having the striped projections and depression thereon. The resin used for the insulation film is not limited to the photosensitive resin. Thermosetting resin and the like may be used for the insulation film.
The insulation film may be formed by a color filtering layer.
This can facilitate the production of the liquid crystal display element including the color filtering layer as set forth in Embodiment 3.
The insulation film may be formed of transparent material.
This can facilitate the production of the liquid crystal display element including the transparent insulation layer as set forth in Embodiment 4.
The above-mentioned objects can be accomplished by the present invention which provides a liquid crystal display element comprising a liquid crystal panel which comprises a pair of substrates and liquid crystals sealed off in between the pair of substrates, and a liquid crystal panel in which pixel electrode parts of pixel electrodes and common electrode parts of common electrodes are alternately formed on a plane of one of the pair of substrates and to change alignment of liquid crystal molecules by generating a horizontal electric field in the plane, wherein at least one of the pixel electrode parts and the common electrode parts has a tapered section with respect to a horizontal electric field direction and is transparent.
With this construction, since the electric field is applied to a region over at least either of the both electrodes parts (the horizontal electric field is applied thereto to a sufficient extent), the liquid crystal molecules over the electrode parts can also be activated and thereby the display characteristics can be improved. Also, since at least one of the both electrodes is transparent, light is prevented from being cut off by the electrode parts. This can produce significantly improved aperture ratio and also can prevent decrease in the aperture ratio even when the distances between the electrode parts are narrowed. This enables the distances between the electrodes to be narrowed, thus producing increased speed of response of the liquid crystals.
The pixel electrode parts or the common electrode parts may have a cone angle of 20 degree or more to less than 90 degree.
The reason for this limitation is that the cone angle of 20 degree or more can produce a large horizontal electric field.
The pixel electrode parts or the common electrode parts may have a cone angle of 20 degree or more to less than 90 degree.
The reason for this limitation is that the cone angle of 45 degree or more can produce a significantly large horizontal electric field.
A distance between two adjoining electrodes of the pixel electrode parts and the common electrode parts may be limited to not more than 6 xcexcm.
With this limitation, since the transparent electrode parts can allow light to be prevented from being cut off by the electrode parts, the distances between the electrodes can be narrowed, while preventing the reduction of aperture ration. Thus, the speed of response of the liquid crystals can be increased so that moving images can be well displayed.
The pixel electrode parts or the common electrode parts may have a triangular section with respect to a horizontal electric field direction.
With this construction, since at least either of the both electrode parts has a triangular section having a taper such that the electric field can be applied to the region over the electrodes (the horizontal electric field is applied thereto to a sufficient extent), the liquid crystal molecules over the electrode parts can also be activated and thereby the display characteristics can be improved. The apex angle at the top of the triangular section is preferably not more than 135 degree, further preferably, not more than 110 degree.
The pixel electrode parts or the common electrode parts may have a trapezium section with respect to a horizontal electric field direction.
With this construction, since at least either of the electrode parts has a trapezium section having a taper such that the electric field can be applied to the region over the electrodes (the horizontal electric field is applied thereto to a sufficient extent), the liquid crystal molecules over the electrode parts can also be activated and thereby the display characteristics can be improved. The smaller the ratio of A/B is, the higher the contrast is, so the ratio of A/B is preferably set to be not more than ⅔, or further preferably not more than xc2xd.
The pixel electrode parts and the common electrode parts may be formed on an insulation film so that the electrode parts and the common electrode parts can be on the same plane.
This arrangement of the insulation film can provide an increased aperture ratio of the liquid crystal display panel and simultaneously an enlarged opposing area of the pixel electrode parts and the common electrode parts. This can allow the horizontal electric field to be easily applied to the liquid crystal molecules to produce promoted activity of the liquid crystal molecules.
The insulation film may have a film thickness of 1 xcexcm or more.
The reasons for this limitation are that the film thickness of the insulation film of 1 xcexcm or more can substantially absorb irregularity of a surface of the substrate forming thereon the insulation film to produce a smooth surface of the insulation film and that the film thickness of 1 xcexcm or more is desirable for reliable insulation performance of the insulation film.
The insulation film may be formed by a color filtering layer.
This structure can eliminate the need to form an additional color filter and thus can eliminate the need for any margin for sticking the color filter on, thus producing a further increased aperture ratio.
The above-mentioned objects can be accomplished by the present invention which provides a liquid crystal display element comprising a liquid crystal panel which comprises a pair of substrates and liquid crystals sealed off in between the pair of substrates and in which pixel electrode parts of pixel electrodes and common electrode parts of common electrodes are alternately formed on a plane of one of the pair of substrates to change alignment of liquid crystal molecules by generating a horizontal electric field in the plane, wherein at least one of the pixel electrode parts and the common electrode parts is formed on a transparent insulation layer having tapered section with respect to a horizontal electric field direction and is formed by transparent conductive film.
With this construction, since the electric field is applied to a region over at least either of the both electrodes parts (the horizontal electric field is applied thereto to a sufficient extent), the liquid crystal molecules over the electrode parts can also be activated and thereby the display characteristics can be improved. Also, since at least one of the both electrodes is transparent, light is prevented from being cut off by the electrode parts, thus producing significantly improved aperture ratio. In addition, since at least either of the pixel electrode parts and the common electrode pars are formed in a film-like form on the a transparent insulation layer having tapered section with respect to a horizontal electric field direction, electric resistance is reduced, so that the electric field is applied to the liquid crystal molecules with ease, to activate the liquid crystal molecules with further ease.
A distance between two adjoining electrodes of the pixel electrode parts and the common electrode parts may be limited to not more than 6 xcexcm.
With this limitation, since the transparent electrode parts can allow light to be prevented from being cut off by the electrode parts, the distances between the electrodes can be narrowed, while preventing the reduction of aperture ratio. Thus, increase in the speed of response can be produced so that moving images can be well displayed.
The transparent insulation layer may have a triangular section with respect to a horizontal electric field direction.
With this construction, since the transparent insulation layer has a triangular section with respect to a horizontal electric field direction, the electric field is applied to the region over the electrodes on the transparent insulation layer (in other words, the horizontal electric field is applied thereto to a sufficient extent). This can cause the liquid crystal molecules over the electrode parts to be activated and thereby the display characteristics can be improved. The apex angle at the top of the triangular section is preferably not more than 135 degree, further preferably, not more than 110 degree.
The transparent insulation layer may have a trapezium section with respect to a horizontal electric field direction.
With this construction, since the transparent insulation layer has a trapezium section with respect to a horizontal electric field direction, the electric field is applied to a region over the electrodes on the transparent insulation layer (in other words, the horizontal electric field is applied thereto to a sufficient extent). This causes the liquid crystal molecules over the electrode parts to be activated and thereby the display characteristics can be improved. The smaller the ratio of A/B is, the higher the display performance (contrast) is, so the ratio of A/B is preferably set to be not more than ⅔, or further preferably not more than xc2xd.
The insulation layer may have a cone angle of 20 degree or more to less than 90 degree.
The reason for this limitation is that the cone angle of 20 degree or more can produce a large horizontal electric field.
The insulation layer may have a cone angle of 45 degree or more to less than 90 degree.
The reason for this limitation is that the cone angle of 45 degree or more can produce a significantly large horizontal electric field.
The transparent insulation layer may be formed on an insulation film so that the pixel electrode parts and the common electrode parts formed on the transparent insulation layer can be on the same plane.
This arrangement of the insulation film can provide an increased aperture ratio of the liquid crystal display panel and simultaneously an enlarged opposing area of the pixel electrode parts and the common electrode parts. This can allow the horizontal electric field to be easily applied to the liquid crystal molecules to produce promoted activity of the liquid crystal molecules.
The insulation film may have a film thickness of 1 xcexcm or more.
The reasons for this limitation are that the film thickness of the insulation film of 1 xcexcm or more can substantially absorb irregularity of a surface of the substrate forming thereon the insulation film to produce a smooth surface of the insulation film and that the film thickness of 1 xcexcm or more is desirable for reliable insulation performance of the insulation film.
The insulation film may be formed by a color filtering layer.
This structure can eliminate the need to form any additional color filter and thus can eliminate the need for any margin for sticking the color filter thereon, thus producing a further increased aperture ratio.
The above-mentioned objects can be accomplished by the present invention which provides a method of producing a liquid crystal display element comprising a liquid crystal panel which comprises a pair of substrates and liquid crystals sealed off in between the pair of substrates, and a liquid crystal panel in which pixel electrode parts of pixel electrodes and common electrode parts of common electrodes are alternately formed on a plane of one of the pair of substrates to change alignment of liquid crystal molecules by generating a horizontal electric field in the plane, the producing method comprising: a first step of forming common electrode parts of the common electrodes and the pixel electrode parts of the pixel electrodes; and a second step of forming at least one of the common electrode parts of the common electrodes and the pixel electrode parts of the pixel electrodes to have a tapered section with respect to a horizontal electric field direction.
This method, by which the electrodes having a tapered section with respect to a horizontal electric field direction are formed, can facilitate the production of the liquid crystal display element having the operation and effects as set forth in Embodiment 15.
The above-mentioned objects can be accomplished by the present invention which provides a method of producing a liquid crystal display element comprising a liquid crystal panel which comprises a pair of substrates and liquid crystals sealed off in between the pair of substrates and in which pixel electrode parts of pixel electrodes and common electrode parts of common electrodes are alternately formed on a plane of one of the pair of substrates to change alignment of liquid crystal molecules by generating a horizontal electric field in the plane, the producing method comprising: a first step of forming a transparent insulation layer in a place in which at least one of the common electrode parts of the common electrodes and the pixel electrode parts of the pixel electrodes is formed; a second step of forming the transparent insulation layer to have a tapered section with respect to a horizontal electric field direction; and a third step of forming at least one of the common electrode parts and the pixel electrode parts on the insulation layer.
This method, by which the transparent insulation layer having a tapered section with respect to a horizontal electric field direction is formed and the electrodes are formed on the transparent insulation layer, can facilitate the production of the liquid crystal display element having the operation and effects as set forth in Embodiment 26.
The above-mentioned objects can be accomplished by the present invention which provides a liquid crystal display element in which liquid crystals are sandwiched between at least a pair of substrates and pixel electrodes having a plurality of pixel electrode parts and common electrodes having a plurality of common electrode parts are formed on at least one of the substrates and which changes alignment of liquid crystal molecules by applying a voltage across the pixel electrodes and the common electrodes, characterized in that at least one of electrode parts of the pixel electrodes and/or the common electrodes forms thereon two or more separate projections.
With this construction, the reflected light is prevented from being so directional as to limit the viewing angle. Therefore, the liquid crystal display element of a substantially high aperture ratio and high brightness can be obtained, without spoiling the characteristic of the horizontal electric field application mode (IPS) of a broad viewing angle.
The projections may be made of photosensitive resin material.
This construction can facilitate the production of the liquid crystal display element having the effects mentioned above.
At least one of the projections may be a form of two or more protuberances of different height being combined together.
This construction can bring out the effects mentioned above with increasing effect.
The protuberances may be limited in shape such that light incident on the projections from the same direction can outgo at different outgoing directions.
The protuberances may be different in area from each other.
The projections may each be different in cone angle.
With this construction, the reflected light is prevented from being directional as to limit the viewing angle. Therefore, the liquid crystal display element of a substantially high aperture ratio and high brightness can be obtained, without spoiling the characteristic of the horizontal electric field application mode (IPS) of a broad viewing angle.
At least one of the projections may have a height required to extend between the pair of substrates.
This construction can provide advantages of preventing the array substrate from being damaged by e.g. bead-like spacers moving in the panel and preventing deterioration in contrast and image quality such as distinguishing dazzle resulting from occurrence of chromatic irregularity at the positions of spacers.
The projections may vary in size in accordance with a distance from a center of a pixel.
One of the common electrodes and the pixel electrodes may have the projections which increase in size in accordance with a distance from a center of the pixel and the other of the common electrodes and the pixel electrodes may have the projections which decrease in size in accordance with a distance from a center of the pixel.
With this structure, since a turning direction of the liquid crystal molecules is reversed when a voltage is applied to the liquid crystal molecules, the shift in color tone is offset with each other and thereby dependency of the color tone due to the orientation can be reduced to a large extent. Thus, the coloring that is caused by the conventional horizontal electric field application mode can be prevented.
At least one of the pixel electrodes or the common electrodes may be formed of transparent conductive material.
At least one of the pixel electrodes or the common electrodes may be formed of light reflection functional material.
With this construction, all rays of incident light are allowed to reflect and outgo from the panel, irrespective of angle of incidence. Accordingly, the reflection loss can be decreased and the utility efficiency of light is enhanced. In addition, since similar effect is obtained for the outside light incident from surrounding environment, the utility efficiency of light can further be enhanced.
The above-mentioned objects can be accomplished by the present invention which provides a liquid crystal display element in which liquid crystals are sandwiched between at least a pair of substrates and pixel electrodes having a plurality of pixel electrode parts and common electrodes having a plurality of common electrode parts are formed on at least one of the substrates and which changes alignment of liquid crystal molecules by applying a voltage across the pixel electrodes and the common electrodes, characterized in that at least one electrode parts of the pixel electrodes and/or the common electrodes are formed into such a shape that incident rays of light can reflect diffusely.
At least one of the projections may have a form of two or more protuberances of different height being combined together.
The projections may each be different in cone angle.